Why are we not crushed by the weight of the atmosphere on our shoulders?

We are not crushed by the weight of the atmosphere because atmosphere is a fluid and we are immersed into it. So, according to the Pascal's law the the pressure a each point in a horizontal level is equal in all the direction irrespective of the orientation of a body.

Variation of pressure in term of the height of a fluid medium is given as:

[tex]P=\rho.g.h[/tex]

[tex]\rho=[/tex]density of fluid

g = acceleration due to gravity

h = height of the free surface of the fluid from the immersed object.

And atmosphere has very less variation of pressure with change in height as it is a rare medium fluid and so for a human height there is very negligible variation of pressure at the heat of a human with respect to his toe.